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Equine Viral Arteritis

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Equine viral arteritis (EVA) is a contagious disease in horses caused by the equine

arteritis virus. It is found in horses around the world. This disease is most concerning

for breeders, racehorse owners, and show horse owners because it can severely

impact breeding and the international movement of horses and semen.
While some horses experience no clinical signs or respiratory disease, the disease

can cause pregnant mares to abort. Infected stallions can become carriers and shed

the virus in semen. Mares should be vaccinated prior to breeding to a carrier stallion.

Certain States may require approval of the State animal health official before a

veterinarian can administer the vaccine. Horses must be isolated for a brief period

after receiving the vaccine.

What To Look For

Although many horses will have few or no clinical signs, some horses may

experience severe illness. Look for:

Fever

Depression

Lack of appetite

Respiratory disease, such as nasal discharge or coughing

Swelling of hind limbs or along the underside of the abdomen (particularly

around the genitals)

Hives (localized or generalized)

Abortions or stillbirths in pregnant mares

Decreased fertility in stallions

How To Prevent This Disease

EVA spreads through respiratory secretions (breathing, sneezing) in close contact

settings, such as barns. Infected stallions shed the virus in semen and can transmit

it to mares during breeding, including via artificial insemination. Horses can also pick

up the virus from contaminated objects such as buckets, tack, brushes, shoes, and

clothing.

To prevent or reduce the spread of this virus:

Isolate infected horses and carrier stallions.

Isolate all new horses and horses returning from other farms, sales, events, or

racetracks for 3 to 4 weeks.
Use good hygiene and biosecurity during the breeding season.

If possible, segregate pregnant mares from other horses on the farm and

maintain mares in small groups until they have foaled.

Blood-test all new breeding stallions for the presence of EAV antibodies before

the start of each breeding season. Have the semen of any antibody-positive,

nonvaccinated stallion laboratory-tested to identify any carrier animals.

Vaccinate all noncarrier breeding stallions at least 4 weeks prior to the start of

each breeding season.

Vaccinate mares at least 3 weeks before breeding with a known infected carrier

stallion or with semen from a known carrier.

Follow all vaccine label instructions when vaccinating stallions and mares,

including the recommended isolation period after administering the vaccine to

prevent transmission of the vaccine strain of the virus to other horses.

Isolate mares vaccinated for the first time against EVA from all but known EAV

antibody-positive animals for 3 weeks after they have been bred to a carrier

stallion because they can spread the virus to other horses.

Follow strict hygienic practices when breeding or collecting semen from carrier

stallions to avoid inadvertently transferring the virus to other animals through

indirect contact with virus-contaminated objects.

Consider vaccinating colts (immature male foals) between 6 and 12 months,

especially in breeds where EAV infection is more prevalent such as

Standardbreds and various Warmblood breeds. This practice will reduce their

risk of becoming carriers later.

How It Is Treated

Treatment typically focuses on rest, supportive care, and measures to reduce

swelling and inflammation.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their

veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health,

zoo, or wildlife personnel; and others) report diagnosed or suspected cases of
nationally listed reportable animal diseases to APHIS District Offices and to the State

animal health official as applicable under State reporting regulations. 

Controlling Equine Viral Arteritis

Economic Significance of EVA

EVA can have economic consequences for both the breeding and performance

sectors of the horse industry, including:

Losses due to abortion or disease and death in young foals

Decreased commercial value of stallions that become persistently infected with

the virus

Reduced demand to breed to carrier stallions because of the added expense

and inconvenience involved in vaccinating and isolating mares before and after

breeding

Denied export markets for carrier stallions or virus-positive semen

Reduced export markets for fillies, mares, colts, and geldings, and noncarrier

stallions that test positive for virus antibodies

An EVA outbreak at a racetrack, equestrian event, or horse show can:

Disrupt training schedules

Reduce race or competition entries

Cause the cancellation of races or events

Diagnosing EVA

It's impossible to diagnose EVA based solely on visible clinical signs because they

can look like those of other diseases. The only way to accurately diagnose EVA is

through laboratory testing of appropriate specimens, including:

Certain tissues and fluids, such as nasal secretions

Blood

Semen

Placental and fetal fluids and tissues
Contact your veterinarian to collect appropriate samples for testing a horse with

suspected clinical signs of EVA or potential exposure to the virus.

To determine whether a stallion is a virus carrier, your veterinarian will first take a

blood sample for laboratory testing. Stallions that test positive for virus antibodies

without any history of vaccination against EVA should be considered potential virus

carriers. The semen should then be screened for the virus to determine whether the

stallion is a carrier.

Standards for Detecting, Controlling, and Preventing EVA

APHIS, with input from the United States Animal Health Association, the American

Horse Council, and the American Association of Equine Practitioners, published

Equine Viral Arteritis: Uniform Methods and Rules. This document contains minimum

standards for detecting, controlling, and preventing EVA as well as minimum EVA

requirements for moving horses within the United States.

Recommended Sources for More Information on EVA

Factsheet: Equine Viral Arteritis (The Center for Food Safety and Public Health)

Overview of Equine Viral Arteritis (Merck Manual)

Article: Equine Viral Arteritis (Equine-Reproduction.com)

AAEP Risk-Based Vaccination Guidelines: EVA (American Association of Equine

Practitioners)

AAEP Biosecurity Guidelines for Venereal Diseases (American Association of

Equine Practitioners)